The present invention relates to a transmission vent assembly to venting a vehicular transmission.
In conventional vehicular transmissions, an air vent assembly is provided to allow air to flow into and out of the transmission housing during operation, referred to as transmission breathing. As heat is generated in the transmission, the temperature of the air and hydraulic fluid therein increases, and likewise the internal pressure increases. Without a vent for breathing, the increased internal pressure relative to the atmospheric exterior pressure may force fluid past the housing seals. When the internal temperature decreases relative to the exterior temperature, such as when a vehicle is driven through high water, the pressure differential is reversed and air flows into the transmission through the vent. Without the vent, contaminants such as dirt and water may be drawn into the transmission through the seals.
Thus a vent or breather is typically incorporated in transmissions to minimize pressure differentials between the interior and exterior. When designing the vent, it is desirable to avoid water ingestion into the transmission as this may contaminate the operation of hydraulically-actuated friction devices. Further it is advantageous to avoid transmission fluid vapor from escaping the confines of the transmission and condensing on the outer surface of the transmission housing. This may be perceived as a fluid leak by a customer and also reduces the volume of fluid inside the transmission. Bi-directional flow of air, i.e. flow into and out of the vent assembly, without use of expensive valves, is a sought-after solution to equalize the pressures.
Ease of assembly is also an important consideration. It is desirable to eliminate the need for a threaded hole in the transmission housing for securing the vent assembly in the housing.
The present invention is for a transmission vent assembly which permits free flow of air in and out of the transmission. While allowing free flow of air, the vent assembly resists water ingestion into and oil expulsion out of the transmission.
The transmission vent assembly comprises a vent apparatus and a cap. The vent apparatus has a cylindrical tube portion received in a mounting hole of a transmission housing and a vent body portion integral and adjacent to the tube portion and having an exterior cylindrical surface of greater diameter than the tube-portion. A central bore defining an internal passage extends through a lower end of the tube to an upper surface of the vent body. The central bore has a larger diameter portion defining an open ended pocket formed in the upper surface of the vent body. Disposed in the open ended pocket is a filter to capture and condense fluid vapor and return fluid to the transmission through the internal passage.
The vent body includes a shoulder about the exterior cylindrical surface adjacent the upper surface and a double lead thread about the exterior cylindrical surface initiating at the shoulder and terminating at a lower end of the vent body.
The cap, formed in a cup-shape, is press fittingly disposed over the vent body. The cap has a closed end seated on the upper surface of the vent body and a cylindrical wall extending therefrom about the exterior cylindrical surface of the vent body. The cap and the shoulder cooperate to form an annular air cavity and the cap and the double lead thread cooperate to define a first and a second threaded passage. The cap further includes an outward impression in the closed end which cooperates with the upper surface of the vent body to define a connecting air passage.
Two bi-directional air flow paths extend between the transmission and the atmosphere through the internal passage, the connecting air passage, the annular air cavity, and each of the two threaded passages, for equalizing pressure in the transmission to the atmosphere. The two threaded passages minimize water ingestion into the transmission through pressure suction or by splashing.